Method for producing clay coated paper for pressure sensitive copying paper

ABSTRACT

A method for preparing a clay-coated paper for pressuresensitive copying which comprises, applying to a paper support having a layer of microcapsules containing at least one color former, a slurry comprising an alkali dispersing agent an anionic high molecular weight electrolyte, an electron-acceptive adsorbent clay, and a binder, and product so obtained.

United States Patent [1 1 Hayashi et al.

[ Aug. 19, 1975 METHOD FOR PRODUCING CLAY COATED PAPER FOR PRESSURE SENSITIVE COPYING PAPER [75] Inventors: Takao Hayashi; Hiroharu Matsukawa, both of Fujinomiya,

Japan [73] Assignee: Fuji Photo Film Co., Ltd., Minami- Ashigara, Japan [22] Filed: Feb. 2, 1973 [21] Appl. No.: 328,982

Related US. Application Data [63] Continuation of Ser. No. 83,211, Oct. 22, 1970,

[56] References Cited UNITED STATES PATENTS 3,226,252 12/1965 Hemstock 117/369 3,293,060 12/1966 Harbort 117/369 OTHER PUBLICATIONS Hall, Paper Coating Additives, Monograph No. 25, pp. 53, 54 (1963).

Primary Examiner-Thomas J. Herbert, Jr. Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT A method for preparing a clay-coated paper for pressure-sensitive copying which comprises, applying to a paper support having a layer of microcapsules containing at least one color former, a slurry comprising an alkali dispersing agent an anionic high molecular weight electrolyte, an electron-acceptive adsorbent clay, and a binder, and product so obtained.

13 Claims, No Drawings METHOD FOR PRODUCING CLAY COATED PAPER FOR PRESSURE SENSITIVE COPYING PAPER CROSS-REFERENCE TO RELATED APPLICATIONS This application is a Continuation application of our earlier copending application Ser. No. 83,21 1 filed Oct. 22, 1970, now abandoned, which claims priority from Oct. 22, 1969, based on Japanese Patent Application No. 84537/69.

BACKGROUND OF THE INVENTION The present invention relates to a method for producing clay coated papers used for pressure-sensitive copying papers, and more particularly, to a method of improving properties and activity of a coated clay layer by adding an anionic high molecular weight electrolytic compound to the slurry of clay and binder (e.g., latex) in the production of clay-coated paper for pressuresensitive copying.

The clay-coated paper normally employed for pressure-sensitive copying is generally produced by coating a clay, (e.g., attapulgite, bentonite Japanese acid clay, active clay, or zeolite), and a binder (e.g., styrenebutadiene latex, styrene-butadiene latex-casein or starch, acrylic ester copolymer latex, or acrylic ester copolymer latex-starch or casein) on the surface of a paper. When this clay-coated paper is piled on a capsule-coated paper produced by applying many micro capsules containing an oil solution of a color precursor or former (e.g., crystal violet lactone, or acylated benzoil leucomethylene blue) and locally pressurized with suitable pressure, such as handwriting or typewriting, the pressurized portion of the clay-coated paper is colored. These clay-coated papers contain excess amounts of binder in order that lpicking (stripping off of the clay'coated layer) during printing, may be prevented. In spite of this, commercial clay-coated papers for pressure-sensitive copying are still apt to cause picking during printing, as compared with art paper or coat paper. The reason for this is considered to be dependent upon the clay. This is also apparent from the fact that the dirt is found in the branket of the offset printing machine is not as pronounced after a printing of 6000 sheets of commercial coat paper. In addition, the printed figures remain clear. On the other hand, the dirt found in the branket is extremely noticeable after printing only 3000-4000 sheets of commercial clay-coated paper and the printed images remain unclear. Furthermore, the excess amounts of binder cover the active points of the clay (points to color the color precursor or former) and reduce its activity (color-forming capacity of claycoated paper), which is the most important property of the clay-coated paper. In addition to this, the activity is extremely reduced in relatively short periods of time by exposing the clay-coated paper to air. This will be hereinafter designated as activity reduction by time lapse.

SUMMARY OF THE INVENTION Therefore, the primary object of this invention is to provide a method for producing clay-coated paper for the pressure-sensitive copying having high membrane strength, activity and time lapse activity.

Accordingly, the inventors have now discovered that the amount of binder necessary to obtain clay-coated paper having a high membrane strength can be considerably decreased by adding an anionic high molecular weight electrolyte to the clay slurry. This binder saving effect is especially effective when a metal oxide, such as zinc oxide, aluminum oxide, manganous oxide, or a metal salt, such as magnesium carbonate, magnesium hydroxide, zinc chloride, or aluminum hydroxide is added to the clay slurry or coating composition.

DETAILED DESCRIPTION OF THE INVENTION Among the anionic high molecular weight electrolytes applicable to the present invention are sodium polyacrylate, sodium alginate, carboxymethylcellulose, carboxyethylcellulose, gum arabic, the sodium salt of styrene-maleic anhydride copolymers, sodium polymethylacrylate, sodium polyglutamate, sodium polyasparaginate, sodium polymethacrylate, the sodium salt of butadiene-methacrylate copolymers, sodium salt of methylvinylether-maleic anhydride copolymers, the so dium salt of polyethylene-maleic anhydride copoly mers, pectin, pectinic acid, carboxymethyl starch, starch sulfate, starch phosphate, potassium polyvinylbenzene sulfonate, carboxymethylether of hydroxyethyl-cellulose, sulfuric acid ester and the phosphoric acid ester of hydroxyethyl cellulose.

The above examples of anionic high molecular electrolytes are for the most part sodium salts, but they may be other alkali metal salts such as potassium salt or lithium salt, as well.

The effective amounts of these compounds to be added to the clay are at least 0.2% by weight based on the clay, and preferably, 0.5-5% by weight. The properties of the clay-coated paper for the pressuresensitive copying obtained by this method are not influenced by the program or order of the addition of these compounds to the clay slurry.

The amount of binder latex necessary is 10-20% by weight based on the clay, and is remarkably reduced by the incorporation of anionic high molecular weight electrolyte.

The sodium alginate or sodium polyacrylate among the above-mentioned compounds have been used previously as the dispersing agents for the production of the art paper or coat paper, but have not been used in a similar manner for the production of the clay-coated paper. Caustic soda, caustic potash, or sodium hexamethaphosphate have been the primary dispersing agents employed.

The above-mentioned compounds are not used as the dispersing agent in the present invention but are employed as additives capable of eliciting the following effects.

1. The wet between the clay and the binder is enhanced by adding at least 0.2 wt. of said compounds to the clay, thus increasing the adhesion therebetween.

2. unfavorable influence of the free metallic ions on the latex is eliminated by protecting the metallic ions, thus increasing membrane strength.

Thus, the present invention increases the strength of the membrane coated on the surface of the clay-coated paper for pressure sensitive copying, increases the activity of the clay-coated paper by the reduction of the binder amounts, minimizes the reduction of the time lapse activity and prevents the yellow color change thereof.

A better understanding of the present invention will be attained from the following examples which are EXAMPLE 1 EXAMPLE 2 250 parts of water and 10 parts of a 20% aqueous solution caustic soda as dispersing agent for the Japanese 250 parts of water and 10 parts of a 20% caustic soda 5 acid clay were mixed. Then, 100 parts of Japanese acid solution as the dispersing agent for Japanese acid clay clay was added thereto with stirring to prepare a slurry. were mixed, and then 100 parts of Japanese acid clay To the slurry, 0.8 parts of the sodium salt of a stywas then added to the resulting liquid with stirring. To rene-maleic anhydride copolymer dissolved in parts the resulting slurry, 0.8 parts of sodium alginate disof water was added. After stirring the mixture, parts solved in 10 parts of water was added and then 15 parts 0 (as solid content) of a styrene butadiene latex was furof a styrene-butadiene latex, (as solid content), was ther added to obtain a coating composition. The coatadded to prepare a coating composition. The resulting ing composition was coated on paper in the same mancoating composition was coated on the surface of paper ner as in Example 1 to prepare a clay-coated paper. having a unit weight of 40 parts/m in an amount of 8.5 In comparison with the present invention, a convenpartslm which is calculated based upon the amount of 15 tional method was conducted as follows. dry acid clay. After drying, the material was subjected 250 parts of water and 10 parts of a aqueous to super-calendering, whereby a clay-coated paper for caustic soda solution as a dispersing agent for Japanese pressure-sensitive copying was obtained. acid clay were mixed together. 100 parts of Japanese acid clay was then added to the mixture with stirring. Comparanve Example 20 After agitating the mixture fully, 40 parts of a 10% In comparison with the method of the invention, a aqueous oxidized starch solution and 20 parts, (as solid conventional method was conducted as follows. content), of a styrene-butadiene rubber latex, as the 250 parts of water and 10 parts of a 20% caustic soda binder, were further added to the mixture to obtain the solution as a dispersing agent were mixed and 100 parts coating composition. This composition was then coated of Japanese acid clay was then added with stirring. on the surface of a paper having a ,unit weight of 40 After stirring the mixture sufficiently, 18 parts, (as parts/m in an amount of 8.5 parts/m (calculated on solid content), of a styrene-butadiene latex as a binder the amounts of dried acid clay). was added to prepare a coating composition. This com- The resulting clay-coated paper was subjected to suposition was then coated on a paper having a unit per-calendering to form a clay-coated paper for presweight of 40 parts/m in an amount of 8.5 parts/m The sure-sensitivecopying paper. material was then dried and subjected to super- The amount of binder in the clay coated layer procalendering, whereby a clay-coated paper for pressureduced by the present invention was 15.8 parts to 100 sensitive copying paper was obtained. parts of the acid clay, whereas that in the clay-coated Though an amount of binder contained in the claylayer produced by the comparative method was 24 coated layer of the invention was 15.8 parts to 100 parts to 100 parts of the Japanese acid clay. In spite of parts of Japanese acid clay and was smaller than that these small amounts of binder, the clay-coated paper of of conventional clay-coated paper which contains 22 the present invention had a stronger membrane parts of binder, the strength of membrane was far supestrength, favorable activity, and time-prolonged activrior. Moreover, since the amount of binder was deity, as shown in the following table. [The sodium salt of creased, the activity and the activity after the lapse of styrene-maleic anhydride copolymer was also regarded time thereof were excellent. The results are shown in as the binder component because of binding property the following table: thereof].

Comparative Comparative Example 1 Example Example 2 Example 2 S th f M b A -H+ Strength of Membrane +-H- Offset Printability *B 5000 sheets 3000 sheets Offset Printability 6000 sheets 2500 sheets Activity (D,) *C 0.98 0.85 Activity (D1) Q01 O-83 Activity After the Lapse of Time 85% 75% Activity After the Lapse of 88% 72% *D (D;,/D x 100) Time (D,jD x 100) "A The strength of the membrane was tested by stripping the surface of membrane by means of a printability tester using various types of inks having mutually 511' 231:3 3 ZSZ CESSZQZZIS iicrlifiliiififiiiiii $355232: EXAMPLE 3 denoted by an increase in the sign. B The actual printing test was conducted by means ofa Heidelberg offset printer TO parts Of water and parts Of a aqueous $3.:253351123233,"Lifiil'fifii"iirri iimfiifipl'fii ifiliilrfiit'l caustic soda Solution were added 5 parts of Zinc oxide intdsizzietg in the table, each shows the dirtiness of the branket and the unclearness ti i g p t f J p id l y was h C The activity was measured by contacting the clay-coated paper with a paper further d d to prepare a Slurry. TO th slurry, 1 part, 2111:1523:52222.zpazgzto'zzareiz (as solid of spdrsrp pplysprylssp wss added to form a distinct color on the clay-coated paper. Subsequently, the density of the and, after Stlnll'lg, 1 7 parts, (as SOlld content), Of a color dye at an absorption maximum of 600 my. wave length was measured. (The measured value was indicatedas 0. methyl methacrylate-butadlene copolymer latex was *D The activity after the lapse of time was measured by contacting the papers. One added to th lurr of these papers was a clay-coated paper which was allowed to stand m the atmosphere for 10 days and the other was a capsule-coated paper. 600 Kg/cm of The obtained coating composition was then coated 23:25:$3.128?atxa'zzzssziaszziszbiii'ixaizassrii pp p paper y me same prpppdprp as in Example 1 o 600 m wave length Was measured. The measured value was indicated as D and the activity alter the lapse of time was calculated from a formula of D lD, X 100.

prepare a clay-coated paper for pressure-sensitive copying. In comparison with the present invention, a conventional method was conducted as follows.

250 parts of water and parts of a aqueous caustic soda solution as a dispersing agent were mixed. 5 parts of zinc oxide was subsequently added with further stirring and then 40 parts of a 10% aqueous casein solution and 22 parts, (as solid content), of methyl 5 methacrylate-butadiene copolymer latex were added to prepare a coating composition. The composition so obtained was coated on a paper by the same procedure as in Example 1, to obtain clay-coated paper for pressuresensitive copying.

Though an amount of binder in the clay-coated paper produced by the present invention was 17.8 parts to 100 parts of acid clay (sodium acrylate was regarded as the binder because of the binding property) and was smaller than that of the comparative clay-coated paper which contains 25 parts of binder to 100 parts of acid clay, the membrane strength was stronger. Moreover, since the amount of binder was reduced, the activity and the activity after the lapse of time were excellent. The results are shown in the following table:

Comparative Example 3 Example 3 slurry, 15 parts (as solid content) of a styrenebutadiene latex was added with stirring, followed by the addition of 1 part of sulfate starch dissolved in 10 parts of water. The coating composition obtained, was coated on a paper by the same procedure as in Example 1, to prepare a clay-coated paper for pressure-sensitive copying.

In comparison with the above clay-coated paper of the present invention, the following clay-coated paper was prepared by the same procedure as the above preparation, except that 40 parts of 10% aqueous casein solution was employed instead of one part of sulfate starch dissolved in 10 parts of water. 18 parts (as solid content) of styrene-butadiene latex was also used.

Similar results as with Examples l-4 were obtained and are shown in the following table.

Time (D,]D X 100) 5000 sheets 0.93 82% 3000 sheets 0.82 73% EXAMPLE 4 250 parts of water and 10 parts of a 20% caustic soda solution as a dispersing agent were mixed, and 8 parts of calcium carbonate was then added thereto with stirring. After stirring the resulting mixture, 100 parts of Japanese acid clay was added to prepare a slurry. To this slurry, 1 part of gum arabic dissolved in 10 parts of water and then 15 parts (as solid content) of a styrenebutadiene latex was added to obtain a coating composition. This composition was coated on a paper by the same procedure as in Example 1 to prepare a claycoated paper for pressure-sensitive copying.

In comparison with the above clay-coated paper of the present invention, the following clay-coated paper was prepared by the same procedure as the above preparation, except that 40 parts of a 10% aqueous starch solution was employed instead of one part of gum arabic dissolved in 10 parts of water. 20 parts of a styrenebutadiene latex was also employed.

Similar results as with Examples l-3 were obtained and are shown in the following table:

Comparative Example 4 Example 4 4. 2500 sheets 0.82 74% H- 5000 sheets 0.96 86% Strength of Membrane Ofiset Printability Activity (D Activity After Lapse of Time (D,/D, X 100) EXAMPLE 5 Although the present invention has been adequately described in the foregoing specification and examples included therein, it is readily apparent that various changes and modifications may be made without departing from the scope thereof.

What is claimed is:

1. A method for preparing a clay-coated paper for pressure-sensitive copying which comprises applying to a paper support a slurry comprising an alkali dispersing agent, an anionic high molecular weight electrolyte, an electron-acceptive adsorbent clay, and a binder, said clay being reactive with a color-former to form a distinct color, the concentration of said electrolyte being in the range of from 0.2 to 5.0% by weight, based on the clay, and, said anionic high molecular weight electrolyte being selected from the group consisting of an alkali metal salt of polyacrylate, alginate, a styrenemaleicanhydride copolymer, polyglutamate, polyasparaginate, polymethacrylate, methylvinylether-maleic anhydride copolymers, a butadiene-methacrylate copolymer, a polyethylene-maleic anhydride copolymer, a polyvinylbenzene sulfonate, carboxymethyl cellulose, carboxyethyl cellulose, gum arabic, pectin, pectinic acid, carboxymethyl starch, starch sulfate, starch phosphate, the carboxymethyl-ether of hydroxyethyl cellulose, and the sulfate ester or phosphate ester of a hydroxyethyl cellulose.

2. The method of claim 1 wherein said electrolyte is a sodium or potassium salt.

3. The method of claim 1 wherein the concentration of said electrolyte ranges from 0.5 to 5.0% by weight, based on the clay.

4. The method of claim 1 wherein the concentration of said binder is -20.0% by weight, based upon the clay.

5. A pressure-sensitive copying paper comprising a support paper having coated thereon a layer comprising an alkali dispersing agent, a clay, a binder, and an anionic high molecular weight electrolyte, said clay being reactive with a color-former to form a distinct color, said electrolyte being present in a range of from 0.2 to 5.0% by weight, based on the clay, and said anionic high molecular weight electrolyte being selected from the group consisting of an alkali metal salt of polyacrylate, alginate, a styrene-maleicanhydride copolymer, polyglutamate, polyasparaginate, polymethacrylate, methylvinylether-maleicanhydride copolymers, a

butadiene-methacrylate copolymer, a polyethylenemaleic anhydride copolymer, a polyvinyl-benzene sulfonate, carboxymethyl cellulose, carboxyethyl cellulose, gum arabic, pectin, pectinic acid, carboxymethyl starch, starch sulfate, starch phosphate, the carboxymethyl-ether of hydroxyethyl cellulose, and the sulfate ester or phosphate ester of a hydroxyethyl cellulose.

6. The pressure-sensitive copying paper of claim wherein said electrolyte is a sodium or potassium salt.

7. The pressure-sensitive copying paper of claim 5 wherein the concentration of said electrolyte ranges from 0.5 to 5.0% by weight, based on the clay.

8. The pressure-sensitive copying paper of claim 5 wherein the amount of binder employed is l0.020.0% by weight.

9. The pressure-sensitive copying paper of claim 5 wherein a layer of microcapsules containing a colorformer is present on the clay-coated paper.

10. The pressure-sensitive copying paper assembly wherein said paper comprises a capsule coated paper containing at least one color-former and a clay-coated paper containing a binder and an anionic high molecular weight electrolyte, said clay contacted with said color former to form a distinct color, wherein said electrolyte is a member selected from the group consisting of a sodium or potassium salt of polyacrylate, alginate, carboxymethyl cellulose, carboxyethyl cellulose, gum

claim 10 wherein the concentration of said electrolyte ranges from 0.2 to 5.0%, by weight, of the clay.

12. The pressure-sensitive copying paper assembly of claim 10 wherein the concentration of said electrolyte ranges from 0.5 to 5.0%, by weight, of the clay.

13. The pressure-sensitive copying paper assembly of claim 10 wherein the concentration of binder employed is l0.020.0% by weight, based upon the clay. 

1. A METHOD FOR PREPARING A CLAY-COATED PAPER FOR PRESSURESENSITIVE COPYING WHICH COMPRISES APPLYING TO A PAPER SUPPORT A SLURRY COMPRISING AN ALKALI DISPERSING AGENT, AN ANIONIC HIGH MOLECULAR WEIGHT ELECTROLYTE,AN ELECTRON-ACCEPTIVE ADSORVBENT CLAY, AND A BINDER, SAID CLAY BEING REACTIVE WITH A COLOR-FORMER TO FORM A DISTINCT COLOR, THE CONCENTRATION OF SAID ELECTROLYTE BEING IN THE RANGE OF FROM 0.2 TO 5.0% BY WEIGT, BASE ON THE CLAY, AND, SAID ANIONIC HIGH MOLECULAR WEIGHT ELECTROLYTE BEING SELECTED FROM THE GROUP CONSISTING OF AN ALKYLI METAL SALT OF POLACRYLATE, ALGINATE, A STYRENE-MALECICANYDRIDE COPOLYMER, POLACRYLATE, POLYASPARAGINATE, METHYLVINYLETHER-MALEIC ANHYDRIDE COPOLYMER A BUTADIENE-METHACRYLATE COPOLYMER, A POLETHENE-MALECI ANHYDRIDE ANHYDRIDE COPOLYMER, A POLYVINLBENZENZENE SULFONATE, CARBOXYMETHYL CELLUOSE, CARBOXETYL CELLOSE, GUM ARABIC, PENCTIN ACID, CARBOXYMETHYL STARCH, STARCH SULFATE, STARCH PHOSPHATE, THE CARBOXYMETHYL-ETHER OF HYDROXYL CELLOSE, AND THE SULFATE ESTER OR PHOSPHATE ESTER OF A HYDROXYETHYL CELLOSE.
 2. The method of claim 1 wherein said electrolyte is a sodium or potassium salt.
 3. The method of claim 1 wherein the concentration of said electrolyte ranges from 0.5 to 5.0% by weight, based on the clay.
 4. The method of claim 1 wherein the concentration of said binder is 10.0-20.0% by weight, based upon the clay.
 5. A PRESSURE-SENSTIVE COPYING PAPER COMPRISING ASUPPORT PAPER HAVING COATED THEREON A LAYER COMPRISING AN ALKLU DISPERSING AGENT, A CLAY, A BINDER, AND AN ANIONIC HIGH MOLECULAR WEIGHT ELECTROLYTE, SAID CLAY BEING REACTIVE WIT ACOLORFORMER TO FORM A DISTINCT COLOR, SAID ELECTROLYTE BEING PRESENT IN A RANGE OF FROM 0.2 TO 5.0% BY WEIGHT, BASED ON THE CLAY, AND SAID ANIONIC MOLECULAR WEIGHT ELECTROLYTE BEING SELECTED FROM THE GROUP CONSISTING OF AN ALKALI METAL SALT OF POLYACRYLATE, ALGINATE, A STYRENE-MALEICANYDRIDE COPOLYMER, POLYGLUTAMATE, POLYASPARAGINATE, POLYMETHACRYLATE, METHYLVINYLETHER-MALECANHYDRIDE COPOLYMERS, A BUTADINE-METHA CRYLATE COPOLYMER, A POLYETHYLENE-MALEIC ANHYDRIC COPOLYMER, A POLYVINY-BENZENE SULFONATE, CARBOXYMETHYL CELLOSE, CARBOXYETHYL CELLOSE, GUM ARABIC, PENTIN ACID, CARBOXYMETHYL STARCH, STARCH SULFATE, STARCH PHOSPHATE, THE CARBOXYTHYL-ETHER OF HYDROXYETHYL CELLOSE, AND THE SULFATE ESTER OR PHOSPHATE ESTER OF A HYDROXYETHYL CELLOSE.
 6. The pressure-sensitive copying paper of claim 5 wherein said electrolyte is a sodium or potassium salt.
 7. The pressure-sensitive copying paper of claim 5 wherein the concentration of said electrolyte ranges from 0.5 to 5.0% by weight, based on the clay.
 8. The pressure-sensitive copying paper of claim 5 wherein the amount of binder employed is 10.0-20.0% by weight.
 9. The pressure-sensitive copying paper of claim 5 wherein a layer of microcapsules containing a color-former is present on the clay-coated paper.
 10. The pressure-sensitive copying paper assembly wherein said paper comprises a capsule coated paper containing at least one color-former and a clay-coated paper containing a binder and an anionic high molecular weight electrolyte, said clay contacted with said color former to form a distinct color, wherein said electrolyte is a member selected from the group consisting of a sodium or potassium salt of polyacrylate, alginate, carboxymethyl cellulose, carboxyethyl cellulose, gum arabic, a styrene-maleicanhydride copolymer, polyglutamate, polyasparaginate, polymethacrylate, methylvinylether-maleicanhydride copolymers, a butadiene-methacrylate copolymer, a polyethylene-maleic anhydride copolymer, pectin, pectinic acid, carboxymethyl starch, starch sulfate, starch phosphate, polyvinylbenzene sulfonate, the carboxymethyl-ether of hydroxyethyl cellulose, and the sulfate ester or phosphate ester of a hydroxyethyl cellulose.
 11. The pressure-sensitive copying paper assembly of claim 10 wherein the concentration of said electrolyte ranges from 0.2 to 5.0%, by weight, of the clay.
 12. The pressure-sensitive copying paper assembly of claim 10 wherein the concentration of said electrolyte ranges from 0.5 to 5.0%, by weight, of the clay.
 13. The pressure-sensitive coPying paper assembly of claim 10 wherein the concentration of binder employed is 10.0-20.0% by weight, based upon the clay. 